Hey Cpapp, welcome to riding. Not sure if you've seen this calculator, but I found this Snowboard Sizing Guide, Size Calculator
from a link on this forum.
I'm sure more experienced riders can chime in, but the calculator gives a decent size-estimate and takes things like ability, boot size, weight, and riding style into account.
Regarding the price I would think
that (unless you went used) you would be hard pressed to find boots, bindings, and a board for under 350…. but I could be wrong.